Automatic clutch

ABSTRACT

The invention concerns an automatic clutch in a motor vehicle drive train with a manually operated gearshift. If an accelerator pedal or the like used to control the engine and a vehicle service brake are not activated, the clutch is set at a creeping moment when a gear is engaged and the engine is running. When the service brake is actuated, this creeping moment is maintained for a predetermined time interval, decreased or suppressed in a time-delayed manner.

The invention concerns an automatic clutch in the drive train of a motorvehicle, having a transmission which is manually shifted betweendifferent drive positions or gears, having an adjusting unit whichautomatically actuates the clutch and having a system of sensors whichserves for controlling said adjusting unit, senses (inter alia) driveractuation of a vehicle brake, driver actuation of a control element(e.g. throttle valve) of the engine as well as an activated state of adrive position and sets the clutch to a creeping moment if, with theengine running and the drive position selected, the vehicle brake andthe control element of the engine are unactuated, or releases the clutchif the vehicle brake remains actuated and the control element is notactuated.

In the case of motor vehicles with customary internal combustionengines, a transmission must be arranged in the drive train to allow thetransmission ratio between the speed of the vehicle engine and the speedof the drive wheels to be changed according to the respective travellingspeed and loading of the vehicle. In the case of customarytransmissions, during a change of drive position the power flow betweenengine and drive wheels has to be interrupted by releasing a clutch.

It is known in principle to use automatic clutches for this purpose,i.e. the clutch is automatically released when changing a transmissionstage and is subsequently re-engaged.

To make maneuvering operations easier, it is known in principle to setthe automatic clutch to a light transmissible torque, i.e. a creepingmoment, when a transmission stage has been selected, the engine isrunning and neither the service brake of the vehicle nor a gas pedalserving for controlling the power of the engine, or the like, areactuated. This makes use of the fact that the engines of motor vehiclesnowadays usually have an effective automatic engine control which isable to keep the engine at a minimum speed, generally at the so-calledidling speed, when the gas pedal is unactuated, to be precise even ifthe engine is loaded to varying degrees. On the basis of thetransmission of a creeping moment by the clutch envisaged in this case,the vehicle can start creeping forward or perform a creeping movement,as is desired for maneuvering operations.

According to PATENTS ABSTRACTS OF JAPAN, M-857 Jul. 31, 1989, Vol.13/No. 340, it is known from JP 1-115742 (A) to release the automaticclutch fully after a predetermined time interval in the creeping phasedescribed above.

According to PATENTS ABSTRACTS OF JAPAN, M-1672 Sep. 13, 1994, Vol.18/No. 491, JP 6-159397 (A) shows in this connection that the creepingmoment is to be automatically controlled in a way in which the speed ofthe vehicle engine does not go below a minimum speed.

The object of the invention is thus to improve further the clutchcontrol in maneuvering operations.

This object is achieved according to the invention by the clutch momentbeing slowly reduced when the brake is actuated and the control elementis unactuated.

The invention is based on the general idea that in driving maneuvreswith the gas pedal or the like not actuated, in the event of the brakebeing actuated the clutch can still transmit a certain torque, which issmall in comparison with the achievable braking forces and is alsoreduced sooner or later with respect to the creeping moment transmittedwhen the brake is not actuated and when the gas pedal is unactuated, orbrought to diminishing values. This ensures that the driver caninitially control the travelling speed against the creeping tendency ofthe vehicle by actuating the brake with varying force. At the same time,it is ensured that undesired overloading of the clutch is avoided.

A particular advantage of the invention is that, if the brake isactuated only for a short time during a creeping maneuvre, a torque isconstantly transmitted by the clutch and, when actuation of the brake isended, is available without delay in reproducible intensity, withoutcomplex control measures being necessary for this.

Otherwise, with regard to advantageous features of the invention,reference is made to the claims and the following explanation of thedrawing, on the basis of which particularly preferred embodiments aredescribed.

In the drawing, the single FIGURE shows a schematized representation ofa drive train of a motor vehicle as well as the components essential forthe clutch control.

An internal combustion engine 1 is connected in drive terms via anautomatically actuated clutch 2 and a transmission 3, the drivepositions or gears of which are changed by manual actuation of a shiftlever 4, and a drive shaft 5, for example a cardan shaft, to drivewheels 6 of a motor vehicle, otherwise not represented in any moredetail.

The actuation of the clutch 2 takes place automatically by means of amotorized adjusting unit 7, for the control of which a system of sensorsis provided for monitoring various parameters of driving operation.

This system of sensors comprises a sensor arrangement 8, which isassigned to the transmission 3 or the shift lever 4 and senses thepositions and/or movements of the latter and consequently "knows" therespectively selected drive position or the respectively engaged gear.Also provided is a sensor 9 which senses the position of an elementserving for controlling the power of the engine 1, for example athrottle valve 10 of the air intake system of the engine 1, or a gaspedal (not shown) actuating the throttle valve.

Furthermore, the system of sensors comprises a signalling device 11,which monitors the actuation of a vehicle brake (not shown). Thissignalling device 11 may be formed by a brake light switch, which ispositively actuated on actuation of the vehicle brake for switching onthe brake lights, for example by a driver-actuated brake pedal (notshown).

Finally, the system of sensors comprises a displacement pickup 12, whichis assigned to the adjusting unit 7 and senses the position of thelatter, and consequently a parameter which is analogous to the value ofthe torque which can be transmitted by the automatic clutch 2.

The signals of the sensor arrangement 8, of the sensor 9, of thesignalling device 11 and of the displacement pickup 12 are processed bya control circuit 13, which controls the adjusting unit 7. The controlcircuit 13 also preferably communicates with an engine control 14, whichhas the task, inter alia, of keeping the engine speed at a minimumspeed, for instance the idling speed, to the greatest extentindependently of the loading of the engine. The engine control 14 also"knows" the torque respectively generated by the engine. The controlcircuit 13 otherwise communicates with speed pickups 15, which areassigned to the vehicle wheels. Consequently, the control circuit 13 canalso "detect" the state of movement of the vehicle.

On the basis of the exchange of information with the engine control 14,the control circuit 13 can also determine the moment transmitted in eachcase by the clutch 2 in dependence on the position of the adjusting unit7. At constant travelling speed, the following applies for the momentM_(K) which can be transmitted by the clutch 2:

    M.sub.K= M.sub.Mot- J.sub.Mot dω.sub.MOt /dt,

where M_(Mot) is the torque generated by the engine 1, which is detectedby the engine control 14, J_(Mot) is the moment of inertia of the engine1, which is predetermined by the design of the engine 1, and ω_(Mot) isthe speed of the engine. t denotes time.

Since all engine-related variables can be sensed by the engine control14 and it can be detected from the signals of the speed pickups 15whether the vehicle is travelling at approximately constant speed, thecontrol circuit 13 knows on the basis of its interaction with the enginecontrol 14 and the speed pickups 15 the respective clutch moment M_(K).In addition, the control circuit 13 knows from the signals of thedisplacement pickup 12 the position of the adjusting unit 7, so that theproportionality between the clutch moment M_(K) and the travel of theadjusting unit 7 can also be determined for the control circuit 13. As aresult, the control circuit 13 thus knows the transmissible momentrespectively set at the clutch 2.

If the throttle valve 10 or a gas pedal controlling the throttle valve10 assumes its rest position, i.e. the gas pedal is not actuated, and iffurthermore the signalling device 11 does not generate a braking signal,i.e. the vehicle brake is not actuated, the control circuit 13 controlsthe adjusting unit 7 in such a way that the clutch 2 is able to transmita predetermined creeping moment of, for example, 30 Nm. Consequently,the vehicle has a creeping tendency advantageous for maneuveringoperations.

If the vehicle brake is then actuated, according to a first embodimentof the invention the setting of the clutch 2 remains unchanged for apredetermined delay time. Thereafter, if the brake continues to remainactuated, the clutch moment is reduced, i.e. the clutch is released.

According to a second advantageous embodiment of the invention, when thevehicle brake is actuated the clutch moment can be initially reducedwith respect to the creeping moment, for example to a value whichcorresponds approximately to one third of the creeping moment. Thisreduced transmissible moment is left unchanged for a predetermined timeinterval if the vehicle brake continues to remain actuated. Thereafter,the clutch moment can be increasingly reduced.

Instead of this, it is also possible when the vehicle brake is actuatedto reduce the clutch moment continuously according to a predeterminedramp, so that if the brake remains actuated the clutch moment is slowlyreduced until a fully released state of the clutch 2 is reached.

What is claimed is:
 1. An automatic clutch in a drive train of a motorvehicle, said drive train having a transmission which is manuallyshifted between different drive positions or transmission stages, anadjusting unit which automatically actuates the clutch and a system ofsensors which serves for controlling said adjusting unit, the systemsensing at least driver actuation of a vehicle brake, driver actuationof an engine control element as well as an activated state of a driveposition or transmission stage, wherein the adjusting unit sets theclutch to a creeping moment if, with the engine running, the vehiclebrake and the control element are unactuated, or releases the clutch ifthe vehicle brake remains actuated and the control element is notactuated, and further wherein, when the vehicle brake is actuated, theclutch moment is reduced continuously according to a predetermined ramp,so that if the brake remains actuated the clutch moment is slowlyreduced until a fully released state of the clutch is reached.
 2. Theclutch as claimed in claim 1, wherein when the brake is actuated and thecontrol element is not actuated the creeping moment or a clutch momentreduced with respect to the creeping moment remains set or, with thebrake remaining actuated, is continuously reduced after a predeterminedholding time.
 3. The clutch as claimed in claim 2, wherein the reducedclutch moment is slowly set when the brake is actuated and the controlelement of the engine is unactuated.
 4. The automatic clutch accordingto claim 1, wherein the engine control element is a throttle valve. 5.The automatic clutch according to claim 2, wherein the predeterminedholding time is between 3-5 seconds.
 6. The clutch according to claim 1,wherein a signal generated by a brake light switch is sensed to detectbrake actuation.
 7. A method of operating an automatic clutch in a drivetrain of a motor vehicle having a manually operated gear shift, themethod comprising the acts of:sensing driver actuation of a vehiclebrake; sensing driver actuation of a control element of an engine;sensing an activated state of a gear position of the manually operatedgear shift; setting the automatic clutch to a creeping moment if, with arunning engine, the vehicle brake and the control element areunactuated; releasing the automatic clutch if the vehicle brake remainsactuated and the control element is not actuated; and when the vehiclebrake is actuated continuously, reducing the clutch moment according toa predetermined ramp so that if the brake remains actuated, the clutchmoment is slowly reduced until a fully released state of the clutch isreached.